The invention concerns on the one hand a gripping device, particularly for automatic printing and/or inserting machines, with a first and second gripping element of which at least one gripping element can be moved relative to the other gripping element to grab sheet-like materials such as printed pages as well as with a measuring device for the recording of at least one position of the gripping elements towards each other, and on the other hand a method for recording a relative position of gripping elements within a gripping device.
Gripping devices of the kind described above are used, for example, by banks or insurance companies on machines for the automatic insertion of bank statements or invoices. Such machines take printed pages such as bank statements or invoices individually off a stack, fold them and slide them into an envelope, which is then sealed.
In familiar gripping devices at least one gripping element, for example, is opened with a cam controller or a compressed air cylinder and then closed again with spring elasticity. It could happen that due to a malfunction in the paper feed two or more sheets are grabbed by the gripping device and forwarded for further processing. It could therefore happen that, for example, two bank statements or two invoices that were meant for different customers are wrongly placed in one envelope. Such an error must be absolutely avoided, also in light of data protection issues.
In order to be able to avoid this error, the suggestion was made to attach an additional lever arm on at least one gripping element, which operates one or two limit switches, depending on the opening of the gripping device. The switch positions are evaluated in order to determine whether the gripping device grabbed no sheet, one sheet or more than one sheet.
However, this familiar solution has the disadvantage that the limit switches have complex mechanic adjustment features and have to be readjusted with every order due to changes in paper thickness. Also, the stability of the mechanical system is not sufficient so that the system is unsafe and prone to malfunctions despite complex adjustment procedures.
The invention is based on the task of further developing a gripping device of the kind described above in such a way that it is not prone to malfunctions and that adjustments to different paper thicknesses can be done in a simple maimer.
The problem is resolved with the device by equipping the measuring device with a transmitter and a sensor that is allocated to it for the continuous recording of the relative position between the first and the second gripping element, with the transmitter being arranged in a moveable gripping element and the sensor in a fixed gripping element, or vice versa. The signal emitted by the sensor can then be evaluated in a subsequent evaluating circuit. Due to the continuous recording process of the position between the two gripping elements, the evaluation of the signal can show whetherxe2x80x94as desiredxe2x80x94one sheet orxe2x80x94wronglyxe2x80x94more than one sheet is located between the gripping elements. Mechanical adjustments to changes in paper quality or paper thickness are no longer required.
The measuring device preferably releases an analog signal, the height of which is proportional to a distance formed between the gripping elements.
In a particularly preferred version, the transmitter has the design of a magnet and the sensor that of a Hall effect sensor. Here, the sensor can be arranged in the fixed gripping element and the magnet in or on the moveable gripping element. It is ensured that the magnet exercises an immediate effect on the sensor, i.e. moves closely in front of the sensor so that the position of the moveable gripping element can be recorded continuously.
Depending on whether the gripping device is empty, has grabbed one sheet or several sheets, the magnet reaches a different position with regard to the Hall effect sensor. The Hail effect sensor releases a slightly modified analog electric potential, which is evaluated. Apart from the number of sheets that were grabbed, this analog electric potential is also dependent on the thickness of one sheet.
The sensor is connected to a signal processing device for the purpose of evaluating the signals; the device consists of a compensating circuit, an amplifying circuit and an evaluating circuit. The sensor is connected to a first inlet of the compensating circuit, whose outlet on the one hand is connected to an inlet of the amplifying circuit and on the other hand to a first inlet of the evaluating circuit. The outlet of the amplifying circuit is connected to a second inlet of the evaluating circuit.
In order to compensate for the no-voltage of the sensor, a second inlet of the compensating circuit can be connected to a potentiometer. In this case, adjustment of no-voltage is done manually. In a preferred version, the second inlet of the compensating circuit is connected to a second outlet of the evaluating circuit in order to feed supply voltage from auxiliary circuits. The evaluating circuit releases analog supply voltage from circuits to the compensating circuit. In order to adjust the amount of supply voltage from auxiliary circuits, it is useful to feed the evaluating circuit also the non-amplified differential potential.
It has proven particularly beneficial to use an intelligent sensor with integrated compensating and amplifying circuits. In this sensor, the compensating and amplifying circuits are connected to a logic circuit such as a microprocessor, which in turn is connected to data storage such as EEPROM. The intelligent sensor has the particular advantage that no-voltage is compensated for internally and that amplification can be adjusted internally.
The components are selected by the implemented logic device (CPU), which during calibration of the sensor mounted on the gripping device obtains matching data from an external computer system via a communication line and stores it in a storage medium such as EEPROM. It has also proven beneficial to connect the sensor with a higher machine control system via an evaluating circuit and via a bus such as a CAN bus.
Furthermore, the invention refers to a method for recording a relative position of the gripping elements of a gripping device, which is characterized by the fact that the position of the gripping elements towards each other is continuously recorded, that in accordance with the number of sheet-like materials grabbed between the gripping elements a signal is generated with different signal values, that the signal values are compared to target values and that in the case of a deviation an error message is created. The signal released by the sensor is compensated, amplified and evaluated. During the evaluation process of the signal, the evaluating circuit can be fed auxiliary signals in order to be able to provide the time of the measurement (for example, gripping element closed).
For the adjustment of the evaluating circuit (Teach-In), a zero value UCLOSED is determined in the case of closed gripping elements without sheet-like material and a target value UTARGET in the case of closed gripping elements with sheet-like material. As described above, it is beneficial in certain versions to feed the evaluating circuit an auxiliary signal such as a trigger signal, which is generated when the gripping elements are closed.
On the other hand, a method where the gripping elements are brought into a defined position, preferably a closed position, after the sheet-like material has been filed would be feasible as well. Here, the gripping device can be closed for example on the way back, thus reached a defined position. A new measurement process is triggered with the subsequent opening. The signal emitted by the sensor is preferably determined in an analog-to-digital converter through continuous scanning and preferably further processed in a computer such as a micro-controller. The no-voltage UCLOSED and/or target-value potential UTARGET for a grabbed sheet is preferably determined in a learning phase.